dt-bindings: fixed-regulator: fix compatible enum

Remove 'const:' in the compatible enum. This was breaking
make dt_binding_check since it has more than one compatible string.

Fixes: 9c86d003 ("dt-bindings: regulator: add regulator-fixed-clock binding")
Signed-off-by: Philippe Schenker <philippe.schenker@toradex.com>
Link: https://lore.kernel.org/r/20190923081840.23391-1-philippe.schenker@toradex.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/regulator/fixed-regulator.yaml

@@ -30,8 +30,8 @@ if:
 properties:
   compatible:
     enum:
-      - const: regulator-fixed
-      - const: regulator-fixed-clock
+      - regulator-fixed
+      - regulator-fixed-clock
 
   regulator-name: true